You know, the same question has been bothering me for ages. 

I wonder if its really stereotypical or not but I tend to agree that in most cases, stereotypes are very true - not just in Nepalese, but among Americans too. Take blacks (rowdy, high chances of having a record), Hispanics (poor), Asians(nerdy, no/limited involvement in illegal acts), White (considerate, well-mannered). That said, exceptions occur. Its not a big surprise to see a white man who's pretty inconsiderate or a rich Latino or hell, a very polite black person with a clean record. 

I suppose you could relate to it among Nepalese too. Since I come from a chhetri family, I know how my family members often make remarks about people belonging to other castes - phohori, chotta, andho/debro, chattu, etc. Doesn't necessarily mean that a person that's a [Disallowed String for - castist reference], [Disallowed String for - castist reference], rai, limbu, gurung, 'tallo jaat', thakuri, '[Disallowed String for - castist reference]', [Disallowed String for - castist reference] society portray such characteristics, but even then, its atypical of a person belonging to different castes reflecting a certain distinct characteristic.